PCI: Add a generic weak pcibios_fixup_bus()

Multiple architectures define this as an empty function, and I'm adding
another one as part of the RISC-V port.  Add a __weak version of
pcibios_fixup_bus() and delete the now-obselete ones in a handful of
ports.

The only functional change should be that microblaze used to export
pcibios_fixup_bus().  None of the other architectures exports this, so I
just dropped it.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

arch/arm64/kernel/pci.c

@@ -22,14 +22,6 @@
 #include <linux/pci-ecam.h>
 #include <linux/slab.h>
 
-/*
- * Called after each bus is probed, but before its children are examined
- */
-void pcibios_fixup_bus(struct pci_bus *bus)
-{
-	/* nothing to do, expected to be removed in the future */
-}
-
 /*
  * We don't have to worry about legacy ISA devices, so nothing to do here
  */